1. Field of the Invention
The invention relates generally to garage door openers and specifically to a kit for modifying the drive sprocket in a garage door opener to convert the drive from a high speed drive to a low speed drive.
In the field of garage door openers, there is an interest in providing an opener which will be suitable for as many different types of existing garage doors as is practical and economically feasible. The garage doors for which potential customers may purchase automatic openers differ considerably in the size and weight of the doors and the power required to open them because of their manner of opening or the manner in which the weight of the door is counterbalanced. In attempting to increase the versatility of a garage door opener and, therefore, broaden the market for it, it has been known in the art to provide an opener with means for varying the speed with which the door is opened and closed and, therefore, the power available from a given motor to accomplish the opening and closing. In other words, if the door is opened slowly, the instantaneous force available is greater than if the door is opened more rapidly. This permits increasing the versatility of a garage door opener by merely providing the speed change without having to provide motors having different amounts of power available for opening and closing the door.
2. Description of the Prior Art
One example of a patent disclosing a constant speed motor with means for varying the output drive speed is a U.S. Pat. No. 4,794,731, to Willmott et. al, which is assigned to the same assignee as the present application. The one-piece garage door shown in the '731 patent may require more power to lift than is required for garage doors having multiple hingeably connected panels which slide upwardly on rollers received in two L-shaped channels. In addition, it has been found that opening a one-piece garage door rapidly often causes jerking or vibrations which tend to be destructive of the drive train for opening the door. This condition can be eliminated by opening the one-piece door at a slower rate than is used for the multiple, hinged panel door. As a means of varying the speed of raising and lowering the door, a garage door opener of the '731 patent utilizes a pair of sprockets, one having eight teeth and the other having six teeth, which may be selectively used to drive the continuous or endless chain loop which drives the lever system to raise and lower the garage door. In order to accommodate the use of either of the sprockets available in the '731 patent, there is provided a reversible idler which permits the installer of the door opener to select the idler position which is aligned with one or the other of the two drive sprockets.
One of the problems associated with the garage door opener of the '731 patent is that the dual sprockets are costly and must be included with each and every model sold. Since the portion of the consumers desiring the low speed sprocket for use on the one-piece garage door is relatively small as compared to those who have the sectioned garage doors and desire to use the high speed sprocket, there is an unnecessary premium in providing the extra sprocket with many of the garage door openers made in accordance with the '731 patent.
Accordingly, it would be desirable to eliminate this built-in premium involved in packing the dual sprocket with every garage door opener and instead provide an accessory kit for the consumer who wishes the low speed drive. This kit could be purchased separately to adapt the garage door opener to the low speed sprocket for those consumers who require that feature. It is important to note that the power delivered by the motor to the opener mechanism is on the order cf one-half to three-quarters of a horsepower and that it is delivered through the drive sprocket which engages the continuous chain as discussed above. Accordingly, it is important that the sprocket be keyed or otherwise attached rigidly to the output shaft so that there will be no slippage between the output shaft and the sprocket engaged with the endless chain. It is further noted that the lesser number of consumers require the slow speed sprocket so the conversion kit must include the means of converting the high speed sprocket to the low speed sprocket which will have fewer teeth than the high speed sprocket.
There are examples in the art of multiple speed sprockets as commonly used in bicycles and other applications. In this connection the patents to Martelli U.S. Pat. No. 2,128,425, Oehler U.S. Pat. No. 2,451,690, Paxton U.S. Pat. No. 3,082,637, Brilando U.S. Pat. No. 3,477,303 and Kouzuki U.S. Pat. No. 3,321,040 are noted
Also noted is the U.S. Pat. No. 601,990 to Suter which discloses a large sprocket which is formed with a recess which allows a smaller sprocket to nest within a recess. The smaller sprocket in the Suter patent is completely enclosed by the larger sprocket. There is no means provided to support the larger sprocket other than mounted on the smaller sprocket. None of the prior art disclosures cited above would be suitable for the conversion kit to adapt a high speed garage door opener to low speed operation.